Twin-shaft type comminutors for the reduction of particle size of solid waste material to small particles by shearing, shredding and crushing are well known in the prior art (see, for instance, U.S. Pat. Nos. 5,406,865 and 5,275,342 to Galanty). Typically, such comminutors employ a pair of counter-rotating parallel shafts having sets of cutter disks and spacers fixedly mounted on each shaft, wherein the cutter disks and spacers intermesh at a close clearance with one another. More particularly, the cutting/shearing tips of each cutter disk rotate in close proximity to their opposing spacer to create a cutting and shearing action, the cutter disk sets rotating at a differential speed.
While the comminutors discussed above have been commercially successful for many years, the intermeshed cutter stacks employed thereby do present an inherent problem in that the close spacing of the intermeshed disks leads to blockage of the incoming solid debris and to a reduction in liquid throughput. One attempt to solve this problem involves the use of a larger comminutor (i.e., one large enough to inhibit solids blockage and to achieve the desired liquid throughput). Such a solution is oftentimes not practical due to increased manufacturing costs and/or power consumption.
Other problems with the prior art twin-shaft wastewater comminutors involve their limited ability to feed or grab round or large objects, which are repelled by the cutters or which simply skip across the tops of the two similarly sized cutter stacks. To partially remedy this situation, it has been proposed to increase the width of the input opening of such comminutors, as well as the throat opening size between the cutter stacks. Because the cutter stacks still have relatively small diameters, this proposed solution does not adequately address the problems associated with the feeding of large, round or irregular shapes of waste material.
Another proposed solution involves providing the comminutors with larger diameter cutter disks and shafts which therefore have more space between the cutter disks. The problem with this approach has been that it necessitates the use of larger motors and drives because of the larger cutter disk diameters, which result in the reduction of force at the shredding tip created by its added distance from the center line of the shaft. As all components get larger to support the additional torque, the comminutor becomes more expensive and less efficient.
Yet another solution has been the addition of auxiliary solids diverting screens to divert solids to the cutter disks while allowing the unimpeded flow of liquid therethrough. This design has problems with efficient delivery of solids to the cutters, operational problems and the additional complication of auxiliary screening devices.
Accordingly, there remains a need for a comminutor without the addition of complex auxiliary screening devices and drive components, or the increased power requirements of increasing the cutter disk size of typical comminution units.
In the foregoing circumstances, it is an object of the present invention to provide comminutor with a design intrinsically open to liquid flow.
Another object of the present invention is to provide a comminutor (shredder) that reduces the amount of energy required to shred and grind solids.
A still further object of the present invention is to provide a comminutor (shredder) that eliminates the need for additional rotating shafts, drives or screen diverters in order to handle high liquid flows.
Yet another object of the present invention is to provide a comminutor (shredder) that is capable of handling large or round shaped objects without having a deleterious affect on its durability and/or efficiency.